CN101694942B - Maximum power tracing method - Google Patents

Abstract

The present invention discloses a maximum power tracking method, which detects the output power P of the power generation equipment as the target of maximum power tracking and the control variable X of the output power, and determines the relationship P between the control variable X and the output power P ( x), within the variation range [x _min , x _max ] of the control variable X, take x _io , X′ _opt and X _opt as the critical points and divide it into four areas in turn, and use different grid-connected power P _e in each area, And the grid-connected constant power control is implemented with A _opt as the embedding point, so the method is simple, easy to implement, strong in anti-interference ability, and beneficial to the stable control of the power system.

Description

Maximum power tracing method

(1) technical field

The present invention relates to a kind of maximum power tracing method, specifically is the maximum power tracing method that is applied to wind power generation and solar power system.Maximum power tracing claims MPPT maximum power point tracking again, be Maximum Power Point Tracking, be called for short MPPT, refer to the generating voltage that controller can the detecting real-time generating equipment, and the tracking maximum power value, make system with the highest efficient to charge in batteries or be connected to the grid.

(2) background technology

Along with fast development of society, energy crisis highlights gradually, is rapidly developed based on the generation of electricity by new energy technology of wind power generation and solar power generation.The MPPT technology is one of key technology of grid-connected power generation system, and in short more than ten years, the MPPT method is constantly proposed, and MPPT method commonly used has: constant voltage is followed the trail of (CVT) method, disturbance observation method (P﹠amp; O), admittance method of addition (INC), intermittent scanning, real-time monitoring method.

Different MPPT methods are applicable to different occasions.For example, these need the applicable cases of substantial contribution in space rocket and space station, and the cost of MPPT controller and complexity are important not as its Performance And Reliability.Because controller need and not need under the prerequisite of periodic adjustment in the short as far as possible time, constantly track real maximum power point (MPP), then P﹠amp; O, INC and RCC are more suitable.Solar telephone need rapidly converge to MPP, fuzzy control so, and neural net, RCC is better selection.Again because the load of solar telephone mainly comprises battery, so also can consider load current or voltage maximization approach.

Introduce the principle of several MPPT methods commonly used below in detail:

1) constant voltage method (CVT)

The constant voltage method for tracing is not proper maximum power tracing mode, and it belongs to a kind of curve fit mode, and its operation principle is: by to the analysis of photovoltaic cell output characteristic as can be known, maximum power point generally is positioned at (0.75～0.95) U _Oc(open circuit voltage) or (0.85～0.95) I _ScBetween (short circuit current), the material and the manufacturing process of this characteristic and photovoltaic cell have much relations.If the battery open circuit voltage under the Current Temperatures is known, just can calculate the maximum power point voltage of this moment so,, just can roughly guarantee photovoltaic cell Maximum Power Output under this temperature as long as the output voltage of control photovoltaic cell in this.Maximum power point tracking is reduced to constant voltage follows the trail of (CVT), the theoretical foundation of CVT control that Here it is.

Weighing apparatus voltage method shortcoming is that control precision is poor, and the precision of system's maximum power tracing depends on the reasonability that given magnitude of voltage is selected, the bad adaptability of control.External environment changes when system, and as intensity of sunshine, system was difficult to carry out maximum power point tracking accurately when the photovoltaic cell plate temperature changed.

2) disturbance observation method (P﹠amp; O)

The basic principle of disturbance observation method is to increase a disturbance quantity artificially for the port voltage of photovoltaic cell component, photovoltaic cell power output before and after the disturbance is compared: if the power output of photovoltaic cell increases after the disturbance, then explanation disturbance before this can improve the power output of photovoltaic cell, then continues the output voltage of disturbance photovoltaic battery pack toward identical direction next time; Otherwise, if the power output of photovoltaic cell reduces after the disturbance, illustrate that then disturbance is unfavorable for increasing the power output of photovoltaic cell, next time then toward opposite direction disturbance.

Because disturbance observation method needs carry out disturbance to the port voltage of photovoltaic cell constantly, therefore also have some inevitable shortcomings: during stable state, can only be near maximum power point oscillatory operation, cause the certain power loss, this shortcoming is that the principle by disturbance observation method self is caused, therefore can't avoid completely, can only reduce power loss by the method for choose reasonable disturbance quantity size.

3) increment conductance method (INC)

Photovoltaic array power output P=IV

Both sides get the V differentiate

$\frac{\mathrm{dP}}{\mathrm{dV}}=\frac{d\left(\mathrm{IV}\right)}{V}=I+V\frac{\mathrm{dI}}{\mathrm{dV}}$

Figure of description 1 shows the principle of increment conductance method, as shown:

When $\frac{\mathrm{dP}}{\mathrm{dV}}>0$ The time, V is less than maximum power point voltage V _Max

When $\frac{\mathrm{dP}}{\mathrm{dV}}<0$ The time, V is greater than maximum power point voltage V _Max

When $\frac{\mathrm{dP}}{\mathrm{dV}}=0$ The time, V is maximum power point voltage V _Max

That is: as V during less than maximum power point voltage, $\frac{\mathrm{dI}}{\mathrm{dV}}-\frac{I}{V}>0$

As V during greater than maximum power point voltage, $\frac{\mathrm{dI}}{\mathrm{dV}}-\frac{I}{V}<0$

When V equals maximum power point voltage, $\frac{\mathrm{dI}}{\mathrm{dV}}-\frac{I}{V}=0$

Like this, can basis

With Between relation adjust quiescent potential and realize the tracking of maximum power point.Fig. 2 is the flow chart of increment conductance method.

The major defect of increment conductance method is, because the increment conductance method needs more computing to judge that the control algolithm relative complex is had relatively high expectations to control system when controlling judgement.

4) intermittent scanning

Intermittent scanning realizes that the principle of MPPT is to allow system periodically be operated in one section voltage range (normally 0.75～0.9 times open circuit voltage), note the power output of different operating voltage correspondence, process is calculated, is compared, thereby determines the maximum power point in this scope.This method does not need ceaselessly to search for, as long as periodically repeat said process, but it can not follow the trail of maximum power point timely and effectively, and the computing capability of digital processing chip is had relatively high expectations.

5) monitor method in real time

The monitoring method is to utilize a baby battery module the same with key light photovoltaic array characteristic as the testing tool to system parameters in real time, by measuring the parameters such as open circuit voltage, short circuit current, intensity of sunshine and temperature of baby battery module, utilize the model knowledge of existing photovoltaic cell, come the maximum power point voltage of the real-time photovoltaic cell of analytical calculation, thereby make main array obtain maximum power output.This method needs extra photovoltaic cell, and requires the photovoltaic cell complexity is arranged and precise math model.

(3) summary of the invention

Therefore, the object of the present invention is to provide a kind of maximum power tracing method that can be used for wind generator system and photovoltaic generating system, this method is simple, be convenient to realize, antijamming capability is strong, and helps power system stability control.

The present invention is by the following technical solutions:

This invention maximum power tracing method, it may further comprise the steps:

A) detect as the power output P of the generating equipment of maximum power tracing object and the control variables X of this power output, and determine that this control variables X and described power output P's concerns P (x);

B) determine the mobility scale [x of described control variables X _Min, x _Max] and this scope in the maximum power P of generating equipment _MaxAnd the control variables X of this maximum power correspondence ^*

C) obtain maximum power operating point A _OptAnd control variables X _OptWith according to generating equipment power output-control variables curve acquisition and the corresponding control variables X ' of the equivalent power output of described maximum power operating point _Opt, and the generating equipment Critical Control variate-value X that is incorporated into the power networks _Io

D) the mobility scale [x of control variables _Min, x _Max] with X _Io, X ' _OptAnd X _OptFor critical point is divided into four zones successively, use the different power P that is incorporated into the power networks in each zone _e, and with A _OptCarry out to be incorporated into the power networks for clamped point and decide power control.

Maximum power tracing method according to technical solution of the present invention adopts the clamped method of power can avoid impact and the negative effect of continuous power fluctuation to electrical network effectively, helps the stable operation of whole electric power system, improves its fail safe.On the other hand, generating equipment power out-put characteristic curve is divided into four different intervals, each interval characteristic difference, and adopt different control strategies, simplified control, and because control variables is obtained easily, its control itself is easy to realize.In addition, can clearly learn the generating equipment operate as normal according to power output-control variables curve after, the interval between just said latter two critical point is adopted and decide the power operation, can guarantee the generating equipment Maximum Power Output, the raising economy.

And that be easy to verify is stable operating point A _OptThe place has small signal stability, because above-mentioned curve is for being similar to parabolical hat-shaped, except peak power output point, all corresponding two operating points of all the other each power outputs and since the minimum value of curve to slope between maximum greater than zero, another side is minus, the former correspondence be the irregular operation point, the latter is a stable operating point, decides power control owing to carry out, and is operating in stable operating point A when generating equipment so _OptWhen corresponding irregular operation point is gone up, any microvariations all will make operating point carry out the transition to automatically to have stable A _OptThe point.

This programme can be controlled flexibly by the sample mode and the sampling period that change generating equipment power output and control variables, can avoid the little interference in measure error and the environment effectively, and antijamming capability is strong, reliable, and control flexibly.

Above-mentioned maximum power tracing method, A in the described step c) _OptAcquisition methods be the subtracting in the interval of power output P, get P=P _Opt=(1-δ ₀) P _Max, this power output output point is a maximum power point (mpp), wherein parameter δ ₀For offset electricity generation equipment to the power loss P between electrical network _LossAnd the penalty coefficient of the caused stability of a system of system fluctuation amplitude.

Above-mentioned maximum power tracing method, the power method that is incorporated into the power networks that described step d) adopted is:

1) at control variables X less than X _Io, the power P of electrical network is sent in control _e=0;

2) control variables is more than or equal to X _IoAnd less than X ' _OptThe time, the power P of electrical network is sent in control _e=max (0,2P-(1+ δ) P _Max), wherein δ is the positive number greater than 0;

3) control variables is more than or equal to X ' _OptAnd smaller or equal to X _OptThe time, the power P of electrical network is sent in control _e=(1-δ ₀) P _Max

4) control variables is greater than X _OptThe time, the power P of electrical network is sent in control _e=(1+ δ) P _Max

Above-mentioned maximum power tracing method, getting the sampling period of detecting generating equipment power output P and control variables X in the step a) is T _s, make P (i) and X (i) be the measured value of current time i, P (i-1) and X (i-1) they are the measured value of a last moment i-1, at X (i) 〉=X _IoSituation under:

I. if P (i) ∈ [P _Opt, P _Max], control also keeps P _e=P _Opt

Ii. under the situation that does not satisfy step I, control P _e=max (0,2P (i)-(1+ δ) P _Max) condition be P (i)＞P (i-1) and X (i)＞X (i-1), perhaps P (i)＜P (i-1) and X (i)＜X (i-1);

Iii. under the situation that does not satisfy step I, control P _e=(1+ δ) P _MaxCondition be P (i)＞P (i-1) and X (i)＜X (i-1), perhaps P (i)＜P (i-1) and X (i)＞X (i-1);

Iv. control P _e=P _OptCondition be that if i-1 constantly, operating point is positioned at the interval of step I i control variables and enters the interval of step I ii at i constantly; Perhaps, if i-1 constantly, operating point is positioned at the interval of step I ii control variables and enters the interval of step I i at i constantly; When the arbitrary condition of this two condition satisfies, the maximum power P of generating equipment _MaxThe control variables X of=P (i-1) and this maximum power correspondence ^*=X (i-1).

Above-mentioned maximum power tracing method when the sampling distortion that detects generating equipment power output P and control variables X or above predictive error, strengthens sampling period T _s

Said method, the dynamical equation of employing control variables $\frac{\mathrm{dX}}{\mathrm{dt}}=\frac{1}{M}(P\left(X\right)-P_e)$ Verify the stability of current point.

Above-mentioned maximum power tracing method, described control variables are its outlet direct voltage U when generating equipment is photovoltaic generation equipment _DC, be wind energy conversion system speed of mainshaft ω when being wind power plant _m

(4) description of drawings

Below in conjunction with Figure of description technical scheme of the present invention is further set forth again, made those skilled in the art better understand the present invention, wherein:

Fig. 1 is an increment conductance method schematic diagram.

Fig. 2 is an increment conductance method algorithm flow chart.

Fig. 3 is a maximum power tracing method principle schematic in the embodiment of the invention.

Fig. 4 is a grid-connected photovoltaic electric power station system block diagram.

Fig. 5 is light irradiance change curve and photovoltaic array outlet DC voltage change curve chart, and this figure takes from monitoring instrument, and transverse axis is time shaft (0.02s), longitudinal axis the latter half outlet direct voltage (100V), and the first half is light irradiance (50, limit is 500).

Fig. 6 is that electrical network three-phase phase voltage, photovoltaic plant inject power network current and power, and this figure takes from monitoring instrument, and transverse axis is time shaft (0.02s), and three parts of the longitudinal axis are respectively photovoltaic plant from bottom to up and inject grid power (0.5*10 ⁴), photovoltaic plant injects power network current (± 20), electrical network three-phase phase voltage (± 200).

Fig. 7 is that maximum power tracing method is followed the trail of the maximum power conditional curve in the embodiment of the invention.

Among the figure: 1, photovoltaic array, 2, electric capacity of voltage regulation, 3, the DC-DC converter, 4, the DC-AC converter, 5, filter, 6, transformer, 7, bus, 8, electrical network.

(5) embodiment

With reference to 3, one a kind of maximum power tracing methods of example of Figure of description, it may further comprise the steps:

A) detect as the power output P of the generating equipment of maximum power tracing object and the control variables X of this power output, and determine that this control variables X and described power output P's concerns P (x);

B) determine the mobility scale [x of described control variables X _Min, x _Max] and this scope in the maximum power P of generating equipment _MaxAnd the control variables X of this maximum power correspondence ^*

C) obtain maximum power operating point A _OptAnd control variables X _OptWith according to generating equipment power output-control variables curve acquisition and the corresponding control variables X ' of the equivalent power output of described maximum power operating point _Opt, and the generating equipment Critical Control variate-value that is incorporated into the power networks _Xio

D) the mobility scale [x of control variables _Min, x _Max] with X _Io, X ' _OptAnd X _OptFor critical point is divided into four zones successively, use the different power P that is incorporated into the power networks in each zone _e, and with A _OptCarry out to be incorporated into the power networks for clamped point and decide power control.

Wherein said four zones are defined as I district, II district, III district and IV district successively.

A in the described step c) _OptAcquisition methods be the subtracting in the interval of power output P, get P=P _Opt=(1-δ ₀) P _Max, this power output output point is a maximum power point (mpp), wherein parameter δ ₀For main offset electricity generation equipment to the power loss P between electrical network _LossPenalty coefficient, this penalty coefficient is the taking into account system caused system operation stability that fluctuates also, its value is a constant, can be easy to calculate according to the characteristic of generating equipment, thereby it is more credible that power is followed the trail of.

The power method that is incorporated into the power networks that described step d) adopted is:

1) at control variables X less than X _Io, just the I district controls the power P of sending into electrical network _e=0;

2) control variables is more than or equal to X _IoAnd less than X ' _OptThe time, just the II district controls the power P of sending into electrical network _e=max (0,2P-(1+ δ) P _Max), wherein δ is the positive number greater than 0;

3) control variables is more than or equal to X ' _OptAnd smaller or equal to X _OptThe time, just the III district controls the power P of sending into electrical network _e=(1-δ ₀) P _Max

4) control variables is greater than X _OptThe time, just the IV district controls the power P of sending into electrical network _e=(1+ δ) P _Max

Wherein, III district and IV district carried out decide power control, especially the former, selected have a stable A _Opt, be not only system's good operation stability, and can guarantee that the generating equipment Maximum Power Output is to improve economy.I district and II district do not utilize all power outputs of generating equipment fully again in addition, be stored in and stablize in the electric capacity, so the output of the power in IV district also can guarantee, and be stable.

The generating equipment output characteristic curve is subjected to multiple factor affecting, and (with the photovoltaic array is example, its output characteristic curve is influenced by multiple external condition such as light irradiance, temperature, wind speed) and change constantly, again by this above example step 4) know, enter the IV district or determine P by the moment that IV enters II by the II district by operating point _Max=P (i-1) is difficult to equate with the real maximum power of generating equipment output characteristic curve.Have again, by the elaboration of top maximum power tracing method to power-tongs position formula as can be known, (1+ δ) P _MaxIt is necessary being a bit larger tham the real maximum power of generating equipment output characteristic curve, by the effect that safety factor δ can play this error of compensation is set.

In order to determine the be incorporated into the power networks conversion of power of generating equipment more easily, getting the sampling period of detecting generating equipment power output P and control variables X in the step a) is T _s, make P (i) and X (i) be the measured value of current time i, P (i-1) and X (i-1) they are the measured value of a last moment i-1, at X (i) 〉=X _IoSituation under:

I. if P (i) ∈ [P _Opt, P _Max], control also keeps P _e=P _Opt

Ii. under the situation that does not satisfy step I, control P _e=max (0,2P (i)-(1+ δ) P _Max) condition be P (i)＞P (i-1) and X (i)＞X (i-1), perhaps P (i)＜P (i-1) and X (i)＜X (i-1);

Iii. under the situation that does not satisfy step I, control P _e=(1+ δ) P _MaxCondition be P (i)＞P (i-1) and X (i)＜X (i-1), perhaps P (i)＜P (i-1) and X (i)＞X (i-1);

Iv. control P _e=P _OptCondition be that if i-1 constantly, operating point is positioned at the interval (II district) of step I i control variables and enters the interval (III district) of step I ii at i constantly; Perhaps, if i-1 is constantly, operating point is positioned at the interval of step I ii control variables and enters the interval of step I i constantly at i, when the arbitrary condition of this two condition satisfies, and the maximum power P of generating equipment _MaxThe control variables X of=P (i-1) and this maximum power correspondence ^*=X (i-1).

When the sampling distortion that detects generating equipment power output P and control variables X or above predictive error, strengthen sampling period T _s, can solve little interference in measure error and the environment with simple method.

Adopt the dynamical equation of control variables $\frac{\mathrm{dX}}{\mathrm{dt}}=\frac{1}{M}(P\left(X\right)-P_e)$ Verify the stability of current point.M is relevant with generating equipment in the formula, if photovoltaic generation equipment then refers to the long-pending of electric capacity of voltage regulation C and corresponding control variables.An example in the III district, is implemented and is decided power control strategy P _e=P _OptThe time, generating equipment has two possible operating point A ' _OptAnd A _Opt

With following formula at A ' _OptAnd A _OptThe point place carries out linearisation and obtains:

$\frac{\mathrm{d\&Delta;X}}{\mathrm{dt}}=\frac{1}{M}\frac{\mathrm{dP}}{\mathrm{dX}}\mathrm{\&Delta;X}$

Characteristic equation is:

$\mathrm{\&lambda;}-\frac{1}{M}\frac{\mathrm{dP}}{\mathrm{dX}}=0$

Thereby system has only a real number characteristic root:

$\mathrm{\&lambda;}=\frac{1}{M}\frac{\mathrm{dP}}{\mathrm{dX}}$

At A ' _OptThe operating point place, because $\frac{\mathrm{dP}}{\mathrm{dX}}>0$ Thereby, λ be one greater than 0 real number, also be A ' _OptPoint is the irregular operation point.And at A _OptThe point place, because $\frac{\mathrm{dP}}{\mathrm{dX}}<0$ Thereby, λ be one less than 0 real number, also be A _OptPoint is a stable operating point.Therefore, the A ' in III _OptWhen operation point place, the A that any microvariations all will make operating point carry out the transition to automatically to have stability _OptThe point.

Described control variables is its outlet direct voltage U when generating equipment is photovoltaic generation equipment _DC, be wind energy conversion system speed of mainshaft ω when being wind power plant _m

With photovoltaic generation equipment is example, the embodiment condition enactment: photovoltaic array grid-connected system, system configuration as shown in Figure 4, control variables is the electric capacity of voltage regulation voltage U _DC, the minimum voltage that is incorporated into the power networks is 500V (direct current), δ=0.1, δ ₀=0.03.Light irradiance changes shown in the last figure of Fig. 5

The photovoltaic plant light irradiance changes, and the photovoltaic plant dynamic characteristic changes thereupon, follows the trail of the simulation result of maximum power respectively as Fig. 5, Fig. 6 and shown in Figure 7 according to carrying power clamping type maximum power tracing method.

Little figure below Fig. 5 has shown the variation along with light irradiance, the change procedure of photovoltaic array outlet direct voltage.Light irradiance sports at 1000 o'clock by 0, and photovoltaic array is the electric capacity of voltage regulation charging, and direct voltage rises to 500V about 0.008s, electric station grid connection operation (seeing Fig. 5, Fig. 6).Light irradiance was reduced to 500 o'clock by 1000, and under the control of carrying maximum power tracing method, through about 0.04s, system stable operation is at new point of safes (seeing Fig. 6, Fig. 7).

The present embodiment result verification feasibility and validity of the power that is incorporated into the power networks being carried out clamped maximum power tracing method proposed by the invention.

Claims (4)

1. A method for maximum power tracking, characterized in that it comprises the following steps: a) Detect the output power P of the power generation equipment as the object of maximum power tracking and the control variable X of the output power, and determine the relationship P(x) between the control variable X and the output power P, wherein the control variable X is in the power generation equipment When it is photovoltaic power generation equipment, it is the outlet DC voltage U _DC ; when it is wind power generation equipment, it is the wind turbine spindle speed ω _m ; b) determining the variation range [x _min , x _max ] of the control variable X and the maximum power P _max of the power generation equipment within this range and the control variable X ^* corresponding to the maximum power; c) Obtain the maximum power operating point A _opt and its control variable X _pot , and obtain the control variable X′ _opt corresponding to the equivalent output power of the maximum power operating point according to the power generation equipment output power-control variable curve, and the power generation equipment and Network critical control variable value X _io , where the maximum power operating point A _opt is obtained by taking P=P _opt =(1-δ ₀ )P _max in the decreasing interval of the output power P, and the output power output point is the maximum The power output point, where the parameter δ ₀ is the compensation coefficient for compensating the power loss P _Loss between the power generation equipment and the grid and the system stability caused by the system fluctuation range; d) Divide the variation range [x _min , x _max ] of the control variable into four areas with X _io , X′ _opt and X _opt as critical points, use different grid-connected power P _e in each area, and use A _opt implements grid-connected constant power control for the embedded point, and the method of using different grid-connected power P _e in each area is: 1) When the control variable X is less than X _io , control the power P _e sent into the grid = 0; 2) When the control variable is greater than or equal to X _io but less than X′ _opt , control the power sent to the grid P _e =max(0,2P-(1+δ)P _max ), where δ is a positive number; 3) When the control variable is greater than or equal to X′ _opt and less than or equal to X _opt , control the power P _e sent into the grid = (1-δ ₀ ) P _max ; 4) When the control variable is greater than X _opt , control the power P _e =(1+δ)P _max sent to the grid. 2. The maximum power tracking method according to claim 1, characterized in that: take the sampling period of detecting the output power P of the generating equipment and the control variable X in step a) as T _s , let P(i) and X(i) is the measured value at the current moment i, P(i-1) and X(i-1) are the measured values at the previous moment i-1, in the case of X(i)≥X _io : i. If P(i)∈[P _opt , P _max ], control and keep P _e =P _opt ; ii. In the case of not satisfying step i, the conditions for controlling P _e =max(0, 2P(i)-(1+δ)P _max ) are P(i)>P(i-1) and X(i )>X(i-1), or P(i)<P(i-1) and X(i)<X(i-1); iii. In the case of not satisfying step i, the conditions for controlling P _e =(1+δ)P _max are P(i)>P(i-1) and X(i)<X(i-1), or P(i)<P(i-1) and X(i)>X(i-1); iv. The condition for controlling P _e = P _opt is that, at time i-1, the operating point is located in the interval of the control variable of step ii and enters the interval of step iii at time i; or, if at time i-1, the operating point is located at In the interval of the control variable of step iii and enter the interval of step ii at time i; when any one of the two conditions is met, the maximum power P _max =P(i-1) of the generating equipment and the corresponding control variable X of the maximum power ^* =X(i-1). 3. The maximum power tracking method according to claim 2, characterized in that: when detecting that the output power P of the power generation equipment and the sampling of the control variable X are distorted or exceed a predetermined error, the sampling period T _s is increased. 4. The maximum power tracking method according to claim 3, characterized in that: the dynamic equation of the control variable is adopted in the photovoltaic power generation equipment Verify the stability of the current point, where M is the product of the voltage stabilizing capacitor and the corresponding control variable.

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